1. Field of the Invention
The present invention relates to a process for preparing 1,1,1-trifluorochloroethane and 1,1,1,2-tetrafluoroethane. More particularly, the present invention relates to a process for preparing 1,1,1-trifluorochloroethane by reacting trichloroethylene and hydrogen fluoride and preparing 1,1,1,2-tetrafluoroethane by further fluorinating 1,1,1-trifluorochloroethane.
2. Description of the Related Art
1,1,1,2-Tetrafluoroethane (hereinafter referred to as "R-134a") is a promising substitute for dichlorodifluoromethane (R-12) which is widely used as a refrigerant, and it is highly desired to establish a process for producing R-134a. 1,1,1-Trifluorochloroethane (hereinafter referred to as "R-133a") is useful as an intermediate in the preparation of R-134a or a raw material for the preparation of trifluoroethanol.
Various processes are known for the preparation of R-134a but each process has its own advantages and disadvantages.
For example, in a process comprising reducing CF.sub.3 CCl.sub.2 F (R-114a) with hydrogen, a conversion is high but a life of a catalyst is very short.
In a process comprising reacting trichloroethylene and hydrogen fluoride to obtain R-133a and then fluorinating R-133a with hydrogen fluoride in a gas phase (cf. Japanese Patent Kokai Publication No. 72105/1973), a selectivity is high and a life of a catalyst is long, but the process has the following drawbacks:
1. Since the reaction for fluorinating trichloroethylene is an exothermic reaction which generates a large amount of heat (about 30 Kcal./mole), control of the reaction is difficult. PA1 2. Since, in the fluorination step of R-133a, 1,1-difluorochloroethylene (hereinafter referred to as "R-1122) which forms an azeotropic mixture with R-134a is contained in the reaction mixture, it is difficult to separate R-134a from the reaction mixture.
When R-134a is prepared by the above conventional process, the steps shown in FIG. 1 are employed.
In this process, trichloroethylene and hydrogen fluoride are supplied to a first reactor. A generated gas contains R-133a, unreacted hydrogen fluoride and hydrogen chloride. If the generated gas is introduced directly to a second reactor, R-134a is not produced due to unfavorable equilibrium. Therefore, the gas is introduced in a hydrogen chloride separator to remove hydrogen chloride from the gas. The remaining gas is then supplied to the second reactor and simultaneously a supplement amount of hydrogen fluoride is added. A reaction mixture from the second reactor comprises desired R-134a, unreacted R-133a and hydrogen fluoride, and a mixture of by-products containing R-1122. This reaction mixture is fed to a third reactor in which R-1122 is converted to R-133a, and the reaction mixture is supplied to a refining apparatus in which hydrogen chloride is separated and removed. The residual materials are supplied to a further refining apparatus to recover R-134a, and R-133a and hydrogen fluoride are recycled to the second reactor.
This process requires three reactors, in the first of which, R-133a is formed, in the second of which, R-134a is formed, and in the third of which, R-1122 is reduced. Therefore, the overall apparatus becomes expensive.